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Register a new userTwo-dimensional kinematics and stellar populations of early-type galaxies: First results from the SAURON survey
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We present the SAURON project, which is aimed at studying the morphology, two-dimensional kinematics and stellar populations of a representative sample of elliptical galaxies and spiral bulges. SAURON, a dedicated integral-field spectrograph that is optimized for wide-field observations and has high throughput, was built in Lyon and is now operated at the WHT 4.2m telescope. At present, we have observed approximately two thirds of the seventy-two sample galaxies with SAURON. A comparison with published long-slit measurements demonstrates that the SAURON-data is of equal or better quality, and provides full two-dimensional coverage. The velocity and velocity dispersion fields exhibit a large variety of morphologies: from simple rotating systems to cylindrical, disky and triaxial velocity fields, bars and decoupled cores. Most of these kinematical signatures do not have counterparts in the light distribution. While some galaxies are consistent with axisymmetry, most are more complex systems than assumed previously. This suggests that the kinematical properties of nearby E/S0 galaxies do not agree with the often assumed simplistic two-family model, in which the giant non-rotating triaxial ellipticals are opposed to the fast-rotating axisymmetric faint ellipticals and S0s.
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The SAURON project will deliver two-dimensional spectroscopic data of a sample of nearby early-type galaxies with unprecedented quality. In this paper, we focus on the mapping of their stellar populations using the SAURON data, and present some preliminary results on a few prototypical cases.
We summarise the results and achievements of integral-field spectroscopy of early-type galaxies, observed as part of a survey using both the SAURON and OASIS spectrographs. From the perspective of integral-field spectroscopy, these otherwise smooth and featureless objects show a wealth of structure, both in their stellar kinematics and populations. We focus on the stellar content, and examine properties on both kiloparsec scales with SAURON, and scales of 100s of parsecs with OASIS. These complementary studies reveal two types of kinematically distinct components (KDCs), differing primarily in their intrinsic sizes. In previous studies, KDCs and their host galaxies have generally been found to be unremarkable in other aspects. We show that large KDCs, typical of the well-studied cases, indeed show little or no age differences with their host galaxy. The KDCs detected with the higher spatial-resolution of OASIS are intrinsically smaller and include, in contrast, a significant fraction of young stars. We speculate on the relationship between KDCs and their host galaxies, and the implications for young populations in early-type galaxies.
We measure the stellar populations as a function of radius for 90 early-type galaxies (ETGs) in the MASSIVE survey, a volume-limited integral-field spectroscopic (IFS) galaxy survey targeting all northern-sky ETGs with absolute K-band magnitude M_K < -25.3 mag, or stellar mass M* 4x10^11 M_sun, within 108 Mpc. We are able to measure reliable stellar population parameters for individual galaxies out to 10-20 kpc (1-3 R_e) depending on the galaxy. Focusing on ~R_e (~10 kpc), we find significant correlations between the abundance ratios, sigma, and M* at large radius, but we also find that the abundance ratios saturate in the highest-mass bin. We see a strong correlation between the kurtosis of the line of sight velocity distribution (h4) and the stellar population parameters beyond R_e. Galaxies with higher radial anisotropy appear to be older, with metal-poorer stars and enhanced [alpha/Fe]. We suggest that the higher radial anisotropy may derive from more accretion of small satellites. Finally, we see some evidence for correlations between environmental metrics (measured locally and on >5 Mpc scales) and the stellar populations, as expected if satellites are quenched earlier in denser environments.
We present the stellar and gas kinematics of a sample of 18 nearby late-type spiral galaxies (Hubble types ranging from Sb to Sd), observed with the integral-field spectrograph SAURON at the 4.2-m William Herschel Telescope. SAURON covers the spectral range 4800-5380 A, allowing us to measure the Hbeta, Fe, Mgb absorption features and the emission in the Hbeta line and the [OIII], and [NI] doublets over a 33x41 arcsec field of view. The maps cover the nuclear region of these late-type galaxies and in all cases include the entire bulge. In many cases the stellar kinematics suggests the presence of a cold inner region, as visible from a central drop in the stellar velocity dispersion. The ionised gas is almost ubiquitous and behaves in a complicated fashion: the gas velocity fields often display more features than the stellar ones, including wiggles in the zero-velocity lines, irregular distributions, ring-like structures. The line ratio [OIII]/Hbeta often takes on low values over most of the field, probably indicating a wide-spread star formation.
Using 3.6$mu$m images of 97 early-type galaxies, we develop and verify methodology to measure globular cluster populations from the S$^4$G survey images. We find that 1) the ratio, T$_{rm N}$, of the number of clusters, N$_{rm CL}$, to parent galaxy stellar mass, M$_*$, rises weakly with M$_*$ for early-type galaxies with M$_* > 10^{10}$ M$_odot$ when we calculate galaxy masses using a universal stellar initial mass function (IMF), but that the dependence of T$_{rm N}$ on M$_*$ is removed entirely once we correct for the recently uncovered systematic variation of IMF with M$_*$, and 2) for M$_* < 10^{10}$ M$_odot$ there is no trend between N$_{rm CL}$ and M$_*$, the scatter in T$_{rm N}$ is significantly larger (approaching 2 orders of magnitude), and there is evidence to support a previous, independent suggestion of two families of galaxies. The behavior of N$_{rm CL}$ in the lower mass systems is more difficult to measure because these systems are inherently cluster poor, but our results may add to previous evidence that large variations in cluster formation and destruction efficiencies are to be found among low mass galaxies. The average fraction of stellar mass in clusters is $sim$ 0.0014 for M$_* > 10^{10}$ M$_odot$ and can be as large as $sim 0.02$ for less massive galaxies. These are the first results from the S$^4$G sample of galaxies, and will be enhanced by the sample of early-type galaxies now being added to S$^4$G and complemented by the study of later type galaxies within S$^4$G.
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